SECTION 3 - CHASSIS & TURNTABLE
3120740
– JLG Lift –
3-47
Wear Tolerance
1.
From the underside of the machine, at rear center, with
the upper boom fully elevated and fully retracted, and
tower boom stowed, as shown in Figure 3-33., Swing
Bearing Tolerance Boom Placement (Sheet 1 of 2), using
a magnetic base dial indicator, measure and record the
distance between the swing bearing and turntable. See
Figure 3-36., Swing Bearing Tolerance Measuring Point
2.
At the same point, with the upper boom at horizontal
and fully extended, and the tower boom fully elevated
and fully retracted as shown in Figure 3-34., Swing Bear-
ing Tolerance Boom Placement (Sheet 2 of 2). Using a
magnetic base dial indicator, measure and record the
distance between the swing bearing and turntable. See
Figure 3-36., Swing Bearing Tolerance Measuring Point
3.
If a difference greater than 0.079 in. (2.00 mm) is deter-
mined, the swing bearing should be replaced.
4.
If a difference less than 0.079 in. (2.00 mm) is deter-
mined, and any of the following conditions exist, the
bearing should be removed, disassembled, and
inspected for the following:
a.
Metal particles in the grease.
b.
Increased drive power required.
c.
Noise.
d.
Rough rotation.
5.
If bearing inspection shows no defects, reassemble and
return to service.
THE SWING BEARING IS ONE OF THE MOST CRITICAL POINTS ON AN AERIAL
LIFT. IT IS HERE THAT THE STRESSES OF LIFTING ARE CONCENTRATED, AT THE
CENTER OF ROTATION. BECAUSE OF THIS, PROPER MAINTENANCE OF THE
SWING BEARING BOLTS IS A MUST FOR SAFE OPERATION.
Swing Bearing Replacement
1.
Removal.
a.
From Ground Control station, operate the boom
adequately to provide access to frame opening to
rotary coupling.
NEVER WORK BENEATH THE BOOM WITHOUT FIRST ENGAGING BOOM SAFETY
PROP OR PROVIDING ADEQUATE OVERHEAD SLING SUPPORT AND/OR BLOCK-
ING.
b.
Attach an adequate support sling to the boom and
draw all slack from sling. Prop or block the boom if
feasible.
c.
From inside turntable, remove mounting hardware
which attach rotary coupling retaining yoke brack-
ets to turntable.
HYDRAULIC LINES AND PORTS SHOULD BE CAPPED IMMEDIATELY AFTER DIS-
CONNECTING LINES TO AVOID THE ENTRY OF CONTAMINANTS INTO THE SYS-
TEM.
d.
Tag and disconnect the hydraulic lines from the fit-
tings on the top of the rotary coupling. Use a suit-
able container to retain any residual hydraulic fluid.
Immediately cap lines and ports.
e.
Attach suitable overhead lifting equipment to the
base of the turntable weldment.
f.
Use a suitable tool to scribe a line on the inner race
of the swing bearing and on the underside of the
turntable. This will aid in aligning the bearing upon
installation. Remove the bolts and washers which
attach the turntable to the bearing inner race. Dis-
card the bolts.
g.
Use the lifting equipment to carefully lift the com-
plete turntable assembly from the bearing. Ensure
that no damage occurs to the turntable, bearing or
frame-mounted components.
Figure 3-35. Swing Bolt Feeler Gauge Check
Figure 3-36. Swing Bearing Tolerance Measuring Point
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